Reduction of sampling rates in lidar systems

ABSTRACT

A LIDAR system has a transmitter that outputs a system output signal from the LIDAR system. The LIDAR system also includes electronics that control a frequency of the system output signal over a series of cycles. The cycles include multiple data periods. The electronics change the frequency of the system output signal at a first rate during a first one of the data periods. The electronics change the frequency of the system output signal at a second rate during a second one of the data periods. The second rate is different from the first rate.

FIELD

The invention relates to optical devices. In particular, the inventionrelates to LIDAR systems.

BACKGROUND

Many LIDAR systems include one or more Analog-to-Digital Converters(ADC) that each receives a beating signal. The high frequencies of thesebeating signals requires that the Analog-to-Digital Converters (ADC) besampled at high rates. However, the price and power consumption of thecommercially available Analog-to-Digital Converters (ADC) are directlyrelated to this sampling rate. As a result, the high sampling ratesassociated with the one or more Analog-to-Digital Converters (ADC) inLIDAR systems can make these systems impractical for commercialproduction. As a result, there is a need for practical LIDAR systems.

SUMMARY

A LIDAR system has a transmitter that outputs a system output signalfrom the LIDAR system. The LIDAR system also includes electronics thatcontrol a frequency of the system output signal over a series of cycles.The cycles include multiple data periods. The electronics change thefrequency of the system output signal at a first rate during a first oneof the data periods. The electronics change the frequency of the systemoutput signal at a second rate during a second one of the data periods.The second rate is different from the first rate.

A LIDAR system includes an Analog-to-Digital Converter (ADC) thatreceives a beating signal that beats a first signal against a secondsignal. The first signal is generated from light that has exited fromthe LIDAR system and returned to the LIDAR system after being reflectedby an object located outside of the LIDAR system. The second signal isgenerated from light that has not exited from the LIDAR system. Afrequency of the beating signal has a frequency contribution from aseparation between the LIDAR system and the object. Electronics generatemultiple first possible frequency values that are each a candidate for avalue of the frequency contribution.

Operating a LIDAR system can include receiving a beating signal at anAnalog-to-Digital Converter (ADC). The beating signal beats a firstsignal against a second signal. The first signal is generated from lightthat has exited from the LIDAR system and returned to the LIDAR systemafter being reflected by an object located outside of the LIDAR system.The second signal is generated from light that has not exited from theLIDAR system. A frequency of the beating signal has a frequencycontribution from a separation between the LIDAR system and the object.Operating the LIDAR system can also include generating multiple firstpossible frequency values that are each a candidate for the value of thefrequency contribution.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a topview of a schematic of a LIDAR system that includes orconsists of a LIDAR chip that outputs a LIDAR output signal and receivesa LIDAR input signal on a common waveguide.

FIG. 1B is a topview of a schematic of a LIDAR system that includes orconsists of a LIDAR chip that outputs a LIDAR output signal and receivesa LIDAR input signal on different waveguides.

FIG. 1C is a topview of a schematic of another embodiment of a LIDARsystem that that includes or consists of a LIDAR chip that outputs aLIDAR output signal and receives multiple LIDAR input signals ondifferent waveguides.

FIG. 1D is a topview of a schematic of a LIDAR system that includes aLIDAR chip that receives an outgoing LIDAR signal from a light sourcelocated off the LIDAR chip.

FIG. 2 is a topview of an example of a LIDAR adapter that is suitablefor use with the LIDAR chip of FIG. 1B.

FIG. 3 is a topview of an example of a LIDAR adapter that is suitablefor use with the LIDAR chip of FIG. 1C.

FIG. 4 is a topview of an example of a LIDAR system that includes theLIDAR chip of FIG. 1A and the LIDAR adapter of FIG. 2 on a commonsupport.

FIG. 5A illustrates an example of a processing component suitable foruse with the LIDAR systems.

FIG. 5B provides a schematic of electronics that are suitable for usewith a processing component constructed according to FIG. 5A.

FIG. 5C illustrates another example of a processing component suitablefor use with the LIDAR systems.

FIG. 5D provides a schematic of electronics that are suitable for usewith a processing component constructed according to FIG. 5C.

FIG. 5E is a graph of frequency versus time for one of the channelsincluded in a LIDAR output signal.

FIG. 5F illustrates a frequency spectrum for use with the LIDAR system.

FIG. 6 is a cross-section of portion of a LIDAR chip that includes awaveguide on a silicon-on-insulator platform.

DESCRIPTION

A LIDAR system transmits a system output signal. Light from the systemoutput signal can be reflected by an object located outside of the LIDARsystem. A portion of the reflected light can return to the LIDAR system.The LIDAR system can combine the returned light with another lightsignal to form a beating signal. The LIDAR system uses the beatingsignal to generate a data signal that is an electrical signal and isalso beating. The data signal can be received by an Analog-to-DigitalConverters (ADC) that outputs a digital data signal. The LIDAR systemincludes electronics that use the digital data signal to generate LIDARdata (radial velocity and/or distance between a LIDAR system and anobject external to the LIDAR system).

During operation of the LIDAR system, the LIDAR system proceeds througha series of cycles. During each cycle, the LIDAR system illuminates asample region. The LIDAR data for objects located in the illuminatedsample region can be generated from each cycle. Each cycle includesmultiple data periods and the electronics control the frequency of thesystem output signal during each of the different data periods. Forinstance, in at least two of the data periods, the electronics canchange the frequency of the system output signal for the duration of thedata period. The rate of the frequency change during the two dataperiods can be selected such that the LIDAR data can be successfullyquantified even when the Analog-to-Digital Converters (ADC) areundersampled. As a result, the LIDAR system can undersample the one ormore Analog-to-Digital Converters (ADC). Since undersampling reduces theADC sampling rate required by the LIDAR system relative to prior LIDARsystems. The reduced sampling rates reduce the costs and/or powerconsumption of the LIDAR system.

FIG. 1A is a topview of a schematic of a LIDAR chip that can serve as aLIDAR system or can be included in a LIDAR system that includescomponents in addition to the LIDAR chip. The LIDAR chip can include aPhotonic Integrated Circuit (PIC) and can be a Photonic IntegratedCircuit chip. The LIDAR chip includes a light source 10 that outputs anoutgoing LIDAR signal. A suitable light source 10 includes, but is notlimited to, semiconductor lasers such as External Cavity Lasers (ECLs),Distributed Feedback lasers (DFBs), Discrete Mode (DM) lasers andDistributed Bragg Reflector lasers (DBRs).

The LIDAR chip also includes a utility waveguide 12 that receives theoutgoing LIDAR signal from the light source 10. The utility waveguide 12terminates at a facet 14 and carries the outgoing LIDAR signal to thefacet 14. The facet 14 can be positioned such that the outgoing LIDARsignal traveling through the facet 14 exits the LIDAR chip and serves asa LIDAR output signal. For instance, the facet 14 can be positioned atan edge of the chip so the outgoing LIDAR signal traveling through thefacet 14 exits the chip and serves as the LIDAR output signal. In someinstances, the portion of the LIDAR output signal that has exited fromthe LIDAR chip can also be considered a system output signal. As anexample, when the exit of the LIDAR output signal from the LIDAR chip isalso an exit of the LIDAR output signal from the LIDAR system, the LIDARoutput signal can also be considered a system output signal. When theportion of the LIDAR output signal serves as a system output signal thefacet 14 can serve as the transmitter of the LIDAR system.

The LIDAR output signal travels away from the LIDAR system through freespace in the atmosphere in which the LIDAR system is positioned. TheLIDAR output signal may be reflected by one or more objects in the pathof the LIDAR output signal. When the LIDAR output signal is reflected,at least a portion of the reflected light travels back toward the LIDARchip as a LIDAR input signal. In some instances, the LIDAR input signalcan also be considered a system return signal. As an example, when theexit of the LIDAR output signal from the LIDAR chip is also an exit ofthe LIDAR output signal from the LIDAR system, the LIDAR input signalcan also be considered a system return signal.

The LIDAR input signals can enter the utility waveguide 12 through thefacet 14. The portion of the LIDAR input signal that enters the utilitywaveguide 12 serves as an incoming LIDAR signal. The utility waveguide12 carries the incoming LIDAR signal to a splitter 16 that moves aportion of the outgoing LIDAR signal from the utility waveguide 12 ontoa comparative waveguide 18 as a comparative signal. The comparativewaveguide 18 carries the comparative signal to a processing component 22for further processing. Although FIG. 1A illustrates a directionalcoupler operating as the splitter 16, other signal tapping componentscan be used as the splitter 16. Suitable splitters 16 include, but arenot limited to, directional couplers, optical couplers, y-junctions,tapered couplers, and Multi-Mode Interference (MIMI) devices.

The utility waveguide 12 also carrier the outgoing LIDAR signal to thesplitter 16. The splitter 16 moves a portion of the outgoing LIDARsignal from the utility waveguide 12 onto a reference waveguide 20 as areference signal. The reference waveguide 20 carries the referencesignal to the processing component 22 for further processing.

The percentage of light transferred from the utility waveguide 12 by thesplitter 16 can be fixed or substantially fixed. For instance, thesplitter 16 can be configured such that the power of the referencesignal transferred to the reference waveguide 20 is an outgoingpercentage of the power of the outgoing LIDAR signal or such that thepower of the comparative signal transferred to the comparative waveguide18 is an incoming percentage of the power of the incoming LIDAR signal.In many splitters 16, such as directional couplers and multimodeinterferometers (MMIs), the outgoing percentage is equal orsubstantially equal to the incoming percentage. In some instances, theoutgoing percentage is greater than 30%, 40%, or 49% and/or less than51%, 60%, or 70% and/or the incoming percentage is greater than 30%,40%, or 49% and/or less than 51%, 60%, or 70%. A splitter 16 such as amultimode interferometers (MMIs) generally provides an outgoingpercentage and an incoming percentage of 50% or about 50%. However,multimode interferometers (MMIs) can be easier to fabricate in platformssuch as silicon-on-insulator platforms than some alternatives. In oneexample, the splitter 16 is a multimode interferometer (MMI) and theoutgoing percentage and the incoming percentage are 50% or substantially50%. As will be described in more detail below, the processing component22 combines the comparative signal with the reference signal to form acomposite signal that carries LIDAR data for a sample region on thefield of view. Accordingly, the composite signal can be processed so asto extract LIDAR data (radial velocity and/or distance between a LIDARsystem and an object external to the LIDAR system) for the sampleregion.

The LIDAR chip can include a control branch for controlling operation ofthe light source 10. The control branch includes a splitter 26 thatmoves a portion of the outgoing LIDAR signal from the utility waveguide12 onto a control waveguide 28. The coupled portion of the outgoingLIDAR signal serves as a tapped signal. Although FIG. 1A illustrates adirectional coupler operating as the splitter 26, other signal tappingcomponents can be used as the splitter 26. Suitable splitters 26include, but are not limited to, directional couplers, optical couplers,y-junctions, tapered couplers, and Multi-Mode Interference (MIMI)devices.

The control waveguide 28 carries the tapped signal to control components30. The control components can be in electrical communication withelectronics 32. During operation, the electronics 32 can adjust thefrequency of the outgoing LIDAR signal in response to output from thecontrol components. An example of a suitable construction of controlcomponents is provided in U.S. patent application Ser. No. 15/977,957,filed on 11 May 2018, entitled “Optical Sensor Chip,” and incorporatedherein in its entirety.

The LIDAR system can be modified so the incoming LIDAR signal and theoutgoing LIDAR signal can be carried on different waveguides. Forinstance, FIG. 1B is a topview of the LIDAR chip of FIG. 1A modifiedsuch that the incoming LIDAR signal and the outgoing LIDAR signal arecarried on different waveguides. The outgoing LIDAR signal exits theLIDAR chip through the facet 14 and serves as the LIDAR output signal.When light from the LIDAR output signal is reflected by an objectexternal to the LIDAR system, at least a portion of the reflected lightreturns to the LIDAR chip as a first LIDAR input signal. The first LIDARinput signals enters the comparative waveguide 18 through a facet 34 andserves as the comparative signal. The comparative waveguide 18 carriesthe comparative signal to a processing component 22 for furtherprocessing. As described in the context of FIG. 1A, the referencewaveguide 20 carries the reference signal to the processing component 22for further processing. As will be described in more detail below, theprocessing component 22 combines the comparative signal with thereference signal to form a composite signal that carries LIDAR data fora sample region on the field of view.

The LIDAR chips can be modified to receive multiple LIDAR input signals.For instance, FIG. 1C illustrates the LIDAR chip of FIG. 1B modified toreceive two LIDAR input signals. A splitter 40 is configured to place aportion of the reference signal carried on the reference waveguide 20 ona first reference waveguide 42 and another portion of the referencesignal on a second reference waveguide 44. Accordingly, the firstreference waveguide 42 carries a first reference signal and the secondreference waveguide 44 carries a second reference signal. The firstreference waveguide 42 carries the first reference signal to a firstprocessing component 46 and the second reference waveguide 44 carriesthe second reference signal to a second processing component 48.Examples of suitable splitters 40 include, but are not limited to,y-junctions, optical couplers, and multi-mode interference couplers(MMIs).

The outgoing LIDAR signal exits the LIDAR chip through the facet 14 andserves as the LIDAR output signal. When light from the LIDAR outputsignal is reflected by one or more object located external to the LIDARsystem, at least a portion of the reflected light returns to the LIDARchip as a first LIDAR input signal. The first LIDAR input signals entersthe comparative waveguide 18 through the facet 34 and serves as a firstcomparative signal. The comparative waveguide 18 carries the firstcomparative signal to a first processing component 46 for furtherprocessing.

Additionally, when light from the LIDAR output signal is reflected byone or more object located external to the LIDAR system, at least aportion of the reflected signal returns to the LIDAR chip as a secondLIDAR input signal. The second LIDAR input signals enters a secondcomparative waveguide 50 through a facet 52 and serves as a secondcomparative signal carried by the second comparative waveguide 50. Thesecond comparative waveguide 50 carries the second comparative signal toa second processing component 48 for further processing.

Although the light source 10 is shown as being positioned on the LIDARchip, all or a portion of the light source 10 can be located off theLIDAR chip. For instance, the utility waveguide 12 can terminate at asecond facet through which the outgoing LIDAR signal can enter theutility waveguide 12 from a light source located off the LIDAR chip. Asan example, FIG. 1D illustrates the LIDAR system of FIG. 1A modified toinclude a light source 10 located off of the LIDAR chip. The utilitywaveguide 12 includes a second facet 53. An optical link 54, such as oneor more optical fibers, carries the outgoing LIDAR signal to the secondfacet 53 of the utility waveguide 12. The optical link 54 is alignedwith the utility waveguide 12 such that an outgoing LIDAR signalgenerated by the light source 10 can enter the utility waveguide 12through the second facet 53. An alignment mechanism 55 such as a fiberblock can provide alignment between the optical link 54 and the utilitywaveguide 12. An optical amplifier 57 can optionally be positioned alongthe optical link so as to amplify the outgoing LIDAR signal. When thelight source is external to the LIDAR chip, suitable light sourcesinclude, but are not limited to, semiconductor lasers such as ExternalCavity Lasers (ECLs), Distributed Feedback lasers (DFBs), Discrete Mode(DM) lasers and Distributed Bragg Reflector lasers (DBRs). In someinstances, the LIDAR system includes one or more lenses (not shown) thatcouple the outgoing LIDAR source into the amplifier 57 or into theutility waveguide 12.

In some instances, a LIDAR chip constructed according to FIG. 1B or FIG.1C is used in conjunction with a LIDAR adapter. In some instances, theLIDAR adapter can be physically optically positioned between the LIDARchip and the one or more reflecting objects and/or the field of view inthat an optical path that the first LIDAR input signal(s) and/or theLIDAR output signal travels from the LIDAR chip to the field of viewpasses through the LIDAR adapter. Additionally, the LIDAR adapter can beconfigured to operate on the first LIDAR input signal and the LIDARoutput signal such that the first LIDAR input signal and the LIDARoutput signal travel on different optical pathways between the LIDARadapter and the LIDAR chip but on the same optical pathway between theLIDAR adapter and a reflecting object in the field of view.

An example of a LIDAR adapter that is suitable for use with the LIDARchip of FIG. 1B is illustrated in FIG. 2. The LIDAR adapter includesmultiple components positioned on a base. For instance, the LIDARadapter includes a circulator 100 positioned on a base 102. Theillustrated optical circulator 100 includes three ports and isconfigured such that light entering one port exits from the next port.For instance, the illustrated optical circulator includes a first port104, a second port 106, and a third port 108. The LIDAR output signalenters the first port 104 from the utility waveguide 12 of the LIDARchip and exits from the second port 106.

The LIDAR adapter can be configured such that the output of the LIDARoutput signal from the second port 106 can also serve as the output ofthe LIDAR output signal from the LIDAR adapter and accordingly from theLIDAR system. As a result, the LIDAR output signal can be output fromthe LIDAR adapter such that the LIDAR output signal is traveling towarda sample region in the field of view. Accordingly, in some instances,the portion of the LIDAR output signal that has exited from the LIDARadapter can also be considered the system output signal. As an example,when the exit of the LIDAR output signal from the LIDAR adapter is alsoan exit of the LIDAR output signal from the LIDAR system, the LIDARoutput signal can also be considered a system output signal. When theLIDAR output signal serves as a system output signal, the second port106 can serve as a transmitter for the LIDAR system.

The LIDAR output signal output from the LIDAR adapter includes, consistsof, or consists essentially of light from the LIDAR output signalreceived from the LIDAR chip. Accordingly, the LIDAR output signaloutput from the LIDAR adapter may be the same or substantially the sameas the LIDAR output signal received from the LIDAR chip. However, theremay be differences between the LIDAR output signal output from the LIDARadapter and the LIDAR output signal received from the LIDAR chip. Forinstance, the LIDAR output signal can experience optical loss as ittravels through the LIDAR adapter and/or the LIDAR adapter canoptionally include an amplifier configured to amplify the LIDAR outputsignal as it travels through the LIDAR adapter.

When one or more objects in the sample region reflect the LIDAR outputsignal, at least a portion of the reflected light travels back to thecirculator 100 as a system return signal. The system return signalenters the circulator 100 through the second port 106. FIG. 2illustrates the LIDAR output signal and the system return signaltraveling between the LIDAR adapter and the sample region along the sameoptical path.

The system return signal exits the circulator 100 through the third port108 and is directed to the comparative waveguide 18 on the LIDAR chip.Accordingly, all or a portion of the system return signal can serve asthe first LIDAR input signal and the first LIDAR input signal includesor consists of light from the system return signal. Accordingly, theLIDAR output signal and the first LIDAR input signal travel between theLIDAR adapter and the LIDAR chip along different optical paths.

As is evident from FIG. 2, the LIDAR adapter can include opticalcomponents in addition to the circulator 100. For instance, the LIDARadapter can include components for directing and controlling the opticalpath of the LIDAR output signal and the system return signal. As anexample, the adapter of FIG. 2 includes an optional amplifier 110positioned so as to receive and amplify the LIDAR output signal beforethe LIDAR output signal enters the circulator 100. The amplifier 110 canbe operated by the electronics 32 allowing the electronics 32 to controlthe power of the LIDAR output signal.

FIG. 2 also illustrates the LIDAR adapter including an optional firstlens 112 and an optional second lens 114. The first lens 112 can beconfigured to couple the LIDAR output signal to a desired location. Insome instances, the first lens 112 is configured to focus or collimatethe LIDAR output signal at a desired location. In one example, the firstlens 112 is configured to couple the LIDAR output signal on the firstport 104 when the LIDAR adapter does not include an amplifier 110. Asanother example, when the LIDAR adapter includes an amplifier 110, thefirst lens 112 can be configured to couple the LIDAR output signal onthe entry port to the amplifier 110. The second lens 114 can beconfigured to couple the LIDAR output signal at a desired location. Insome instances, the second lens 114 is configured to focus or collimatethe LIDAR output signal at a desired location. For instance, the secondlens 114 can be configured to couple the LIDAR output signal the on thefacet 34 of the comparative waveguide 18.

The LIDAR adapter can also include one or more direction changingcomponents such as mirrors. FIG. 2 illustrates the LIDAR adapterincluding a mirror as a direction-changing component 116 that redirectsthe system return signal from the circulator 100 to the facet 20 of thecomparative waveguide 18.

The LIDAR chips include one or more waveguides that constrains theoptical path of one or more light signals. While the LIDAR adapter caninclude waveguides, the optical path that the system return signal andthe LIDAR output signal travel between components on the LIDAR adapterand/or between the LIDAR chip and a component on the LIDAR adapter canbe free space. For instance, the system return signal and/or the LIDARoutput signal can travel through the atmosphere in which the LIDAR chip,the LIDAR adapter, and/or the base 102 is positioned when travelingbetween the different components on the LIDAR adapter and/or between acomponent on the LIDAR adapter and the LIDAR chip. As a result, opticalcomponents such as lenses and direction changing components can beemployed to control the characteristics of the optical path traveled bythe system return signal and the LIDAR output signal on, to, and fromthe LIDAR adapter.

Suitable bases 102 for the LIDAR adapter include, but are not limitedto, substrates, platforms, and plates. Suitable substrates include, butare not limited to, glass, silicon, and ceramics. The components can bediscrete components that are attached to the substrate. Suitabletechniques for attaching discrete components to the base 102 include,but are not limited to, epoxy, solder, and mechanical clamping. In oneexample, one or more of the components are integrated components and theremaining components are discrete components. In another example, theLIDAR adapter includes one or more integrated amplifiers and theremaining components are discrete components.

The LIDAR system can be configured to compensate for polarization. Lightfrom a laser source is typically linearly polarized and hence the LIDARoutput signal is also typically linearly polarized. Reflection from anobject may change the angle of polarization of the returned light.Accordingly, the system return signal can include light of differentlinear polarization states. For instance, a first portion of a systemreturn signal can include light of a first linear polarization state anda second portion of a system return signal can include light of a secondlinear polarization state. The intensity of the resulting compositesignals is proportional to the square of the cosine of the angle betweenthe comparative and reference signal polarization fields. If the angleis 90 degrees, the LIDAR data can be lost in the resulting compositesignal. However, the LIDAR system can be modified to compensate forchanges in polarization state of the LIDAR output signal.

FIG. 3 illustrates the LIDAR system of FIG. 3 modified such that theLIDAR adapter is suitable for use with the LIDAR chip of FIG. 1C. TheLIDAR adapter includes a beamsplitter 120 that receives the systemreturn signal from the circulator 100. The beamsplitter 120 splits thesystem return signal into a first portion of the system return signaland a second portion of the system return signal. Suitable beamsplittersinclude, but are not limited to, Wollaston prisms, and MEMS-basedbeamsplitters.

The first portion of the system return signal is directed to thecomparative waveguide 18 on the LIDAR chip and serves as the first LIDARinput signal described in the context of FIG. 1C. The second portion ofthe system return signal is directed a polarization rotator 122. Thepolarization rotator 122 outputs a second LIDAR input signal that isdirected to the second input waveguide 76 on the LIDAR chip and servesas the second LIDAR input signal.

The beamsplitter 120 can be a polarizing beam splitter. One example of apolarizing beamsplitter is constructed such that the first portion ofthe system return signal has a first polarization state but does nothave or does not substantially have a second polarization state and thesecond portion of the system return signal has a second polarizationstate but does not have or does not substantially have the firstpolarization state. The first polarization state and the secondpolarization state can be linear polarization states and the secondpolarization state is different from the first polarization state. Forinstance, the first polarization state can be TE and the secondpolarization state can be TM or the first polarization state can be TMand the second polarization state can be TE. In some instances, thelaser source can linearly polarized such that the LIDAR output signalhas the first polarization state. Suitable beamsplitters include, butare not limited to, Wollaston prisms, and MEMs-based polarizingbeamsplitters.

A polarization rotator can be configured to change the polarizationstate of the first portion of the system return signal and/or the secondportion of the system return signal. For instance, the polarizationrotator 122 shown in FIG. 3 can be configured to change the polarizationstate of the second portion of the system return signal from the secondpolarization state to the first polarization state. As a result, thesecond LIDAR input signal has the first polarization state but does nothave or does not substantially have the second polarization state.Accordingly, the first LIDAR input signal and the second LIDAR inputsignal each have the same polarization state (the first polarizationstate in this example). Despite carrying light of the same polarizationstate, the first LIDAR input signal and the second LIDAR input signalare associated with different polarization states as a result of the useof the polarizing beamsplitter. For instance, the first LIDAR inputsignal carries the light reflected with the first polarization state andthe second LIDAR input signal carries the light reflected with thesecond polarization state. As a result, the first LIDAR input signal isassociated with the first polarization state and the second LIDAR inputsignal is associated with the second polarization state.

Since the first LIDAR input signal and the second LIDAR carry light ofthe same polarization state, the comparative signals that result fromthe first LIDAR input signal have the same polarization angle as thecomparative signals that result from the second LIDAR input signal.

Suitable polarization rotators include, but are not limited to, rotationof polarization-maintaining fibers, Faraday rotators, half-wave plates,MEMs-based polarization rotators and integrated optical polarizationrotators using asymmetric y-branches, Mach-Zehnder interferometers andmulti-mode interference couplers.

Since the outgoing LIDAR signal is linearly polarized, the firstreference signals can have the same linear polarization state as thesecond reference signals. Additionally, the components on the LIDARadapter can be selected such that the first reference signals, thesecond reference signals, the comparative signals and the secondcomparative signals each have the same polarization state. In theexample disclosed in the context of FIG. 3, the first comparativesignals, the second comparative signals, the first reference signals,and the second reference signals can each have light of the firstpolarization state.

As a result of the above configuration, first composite signalsgenerated by the first processing component 46 and second compositesignals generated by the second processing component 48 each resultsfrom combining a reference signal and a comparative signal of the samepolarization state and will accordingly provide the desired beatingbetween the reference signal and the comparative signal. For instance,the composite signal results from combining a first reference signal anda first comparative signal of the first polarization state and excludesor substantially excludes light of the second polarization state or thecomposite signal results from combining a first reference signal and afirst comparative signal of the second polarization state and excludesor substantially excludes light of the first polarization state.Similarly, the second composite signal includes a second referencesignal and a second comparative signal of the same polarization statewill accordingly provide the desired beating between the referencesignal and the comparative signal. For instance, the second compositesignal results from combining a second reference signal and a secondcomparative signal of the first polarization state and excludes orsubstantially excludes light of the second polarization state or thesecond composite signal results from combining a second reference signaland a second comparative signal of the second polarization state andexcludes or substantially excludes light of the first polarizationstate.

The above configuration results in the LIDAR data for a single sampleregion in the field of view being generated from multiple differentcomposite signals (i.e. first composite signals and the second compositesignal) from the sample region. In some instances, determining the LIDARdata for the sample region includes the electronics combining the LIDARdata from different composite signals (i.e. the composite signals andthe second composite signal). Combining the LIDAR data can includetaking an average, median, or mode of the LIDAR data generated from thedifferent composite signals. For instance, the electronics can averagethe distance between the LIDAR system and the reflecting objectdetermined from the composite signal with the distance determined fromthe second composite signal and/or the electronics can average theradial velocity between the LIDAR system and the reflecting objectdetermined from the composite signal with the radial velocity determinedfrom the second composite signal.

In some instances, determining the LIDAR data for a sample regionincludes the electronics identifying one or more composite signals (i.e.the composite signal and/or the second composite signal) as the sourceof the LIDAR data that is most represents reality (the representativeLIDAR data). The electronics can then use the LIDAR data from theidentified composite signal as the representative LIDAR data to be usedfor additional processing. For instance, the electronics can identifythe signal (composite signal or the second composite signal) with thelarger amplitude as having the representative LIDAR data and can use theLIDAR data from the identified signal for further processing by theLIDAR system. In some instances, the electronics combine identifying thecomposite signal with the representative LIDAR data with combining LIDARdata from different LIDAR signals. For instance, the electronics canidentify each of the composite signals with an amplitude above anamplitude threshold as having representative LIDAR data and when morethan two composite signals are identified as having representative LIDARdata, the electronics can combine the LIDAR data from each of identifiedcomposite signals. When one composite signal is identified as havingrepresentative LIDAR data, the electronics can use the LIDAR data fromthat composite signal as the representative LIDAR data. When none of thecomposite signals is identified as having representative LIDAR data, theelectronics can discard the LIDAR data for the sample region associatedwith those composite signals.

Although FIG. 3 is described in the context of components being arrangedsuch that the first comparative signals, the second comparative signals,the first reference signals, and the second reference signals each havethe first polarization state, other configurations of the components inFIG. 3 can arranged such that the composite signals result fromcombining a reference signal and a comparative signal of the same linearpolarization state and the second composite signal results fromcombining a reference signal and a comparative signal of the same linearpolarization state. For instance, the beamsplitter 120 can beconstructed such that the second portion of the system return signal hasthe first polarization state and the first portion of the system returnsignal has the second polarization state, the polarization rotatorreceives the first portion of the system return signal, and the outgoingLIDAR signal can have the second polarization state. In this example,the first LIDAR input signal and the second LIDAR input signal each hasthe second polarization state.

The above system configurations result in the first portion of thesystem return signal and the second portion of the system return signalbeing directed into different composite signals. As a result, since thefirst portion of the system return signal and the second portion of thesystem return signal are each associated with a different polarizationstate but electronics can process each of the composite signals, theLIDAR system compensates for changes in the polarization state of theLIDAR output signal in response to reflection of the LIDAR outputsignal.

The LIDAR adapter of FIG. 3 can include additional optical componentsincluding passive optical components. For instance, the LIDAR adaptercan include an optional third lens 126. The third lens 126 can beconfigured to couple the second LIDAR output signal at a desiredlocation. In some instances, the third lens 126 focuses or collimatesthe second LIDAR output signal at a desired location. For instance, thethird lens 126 can be configured to focus or collimate the second LIDARoutput signal on the facet 52 of the second comparative waveguide 50.The LIDAR adapter also includes one or more direction changingcomponents 124 such as mirrors and prisms. FIG. 3 illustrates the LIDARadapter including a mirror as a direction changing component 124 thatredirects the second portion of the system return signal from thecirculator 100 to the facet 52 of the second comparative waveguide 50and/or to the third lens 126.

When the LIDAR system includes a LIDAR chip and a LIDAR adapter, theLIDAR chip, electronics, and the LIDAR adapter can be positioned on acommon mount. Suitable common mounts include, but are not limited to,glass plates, metal plates, silicon plates and ceramic plates. As anexample, FIG. 4 is a topview of a LIDAR system that includes the LIDARchip and electronics 32 of FIG. 1A and the LIDAR adapter of FIG. 2 on acommon support 140. Although the electronics 32 are illustrated as beinglocated on the common support, all or a portion of the electronics canbe located off the common support. When the light source 10 is locatedoff the LIDAR chip, the light source can be located on the commonsupport 140 or off of the common support 140. Suitable approaches formounting the LIDAR chip, electronics, and/or the LIDAR adapter on thecommon support include, but are not limited to, epoxy, solder, andmechanical clamping.

The LIDAR systems can include components including additional passiveand/or active optical components. For instance, the LIDAR system caninclude one or more components that receive the LIDAR output signal fromthe LIDAR chip or from the LIDAR adapter. The portion of the LIDARoutput signal that exits from the one or more components can serve asthe system output signal. As an example, the LIDAR system can includeone or more beam steering components that receive the LIDAR outputsignal from the LIDAR chip or from the LIDAR adapter and that output allor a fraction of the LIDAR output signal that serves as the systemoutput signal. Suitable beam steering components include, but are notlimited to, movable mirrors, MEMS mirrors, and optical phased arrays(OPAs). In these instances, the one or more components can serve as atransmitter of the system output signal for the LIDAR system.

FIG. 5A through FIG. 5D illustrate an example of a suitable processingcomponent for use as all or a fraction of the processing componentsselected from the group consisting of the processing component 22, thefirst processing component 46 and the second processing component 48.The processing component receives a comparative signal from acomparative waveguide 196 and a reference signal from a referencewaveguide 198. The comparative waveguide 18 and the reference waveguide20 shown in FIG. 1A and FIG. 1B can serve as the comparative waveguide196 and the reference waveguide 198, the comparative waveguide 18 andthe first reference waveguide 42 shown in FIG. 1C can serve as thecomparative waveguide 196 and the reference waveguide 198, or the secondcomparative waveguide 50 and the second reference waveguide 44 shown inFIG. 1C can serve as the comparative waveguide 196 and the referencewaveguide 198.

The processing component includes a second splitter 200 that divides thecomparative signal carried on the comparative waveguide 196 onto a firstcomparative waveguide 204 and a second comparative waveguide 206. Thefirst comparative waveguide 204 carries a first portion of thecomparative signal to the light-combining component 211. The secondcomparative waveguide 208 carries a second portion of the comparativesignal to the second light-combining component 212.

The processing component includes a first splitter 202 that divides thereference signal carried on the reference waveguide 198 onto a firstreference waveguide 204 and a second reference waveguide 206. The firstreference waveguide 204 carries a first portion of the reference signalto the light-combining component 211. The second reference waveguide 208carries a second portion of the reference signal to the secondlight-combining component 212.

The second light-combining component 212 combines the second portion ofthe comparative signal and the second portion of the reference signalinto a second composite signal. Due to the difference in frequenciesbetween the second portion of the comparative signal and the secondportion of the reference signal, the second composite signal is beatingbetween the second portion of the comparative signal and the secondportion of the reference signal.

The second light-combining component 212 also splits the resultingsecond composite signal onto a first auxiliary detector waveguide 214and a second auxiliary detector waveguide 216. The first auxiliarydetector waveguide 214 carries a first portion of the second compositesignal to a first auxiliary light sensor 218 that converts the firstportion of the second composite signal to a first auxiliary electricalsignal. The second auxiliary detector waveguide 216 carries a secondportion of the second composite signal to a second auxiliary lightsensor 220 that converts the second portion of the second compositesignal to a second auxiliary electrical signal. Examples of suitablelight sensors include germanium photodiodes (PDs), and avalanchephotodiodes (APDs).

In some instances, the second light-combining component 212 splits thesecond composite signal such that the portion of the comparative signal(i.e. the portion of the second portion of the comparative signal)included in the first portion of the second composite signal is phaseshifted by 180° relative to the portion of the comparative signal (i.e.the portion of the second portion of the comparative signal) in thesecond portion of the second composite signal but the portion of thereference signal (i.e. the portion of the second portion of thereference signal) in the second portion of the second composite signalis not phase shifted relative to the portion of the reference signal(i.e. the portion of the second portion of the reference signal) in thefirst portion of the second composite signal. Alternately, the secondlight-combining component 212 splits the second composite signal suchthat the portion of the reference signal (i.e. the portion of the secondportion of the reference signal) in the first portion of the secondcomposite signal is phase shifted by 180° relative to the portion of thereference signal (i.e. the portion of the second portion of thereference signal) in the second portion of the second composite signalbut the portion of the comparative signal (i.e. the portion of thesecond portion of the comparative signal) in the first portion of thesecond composite signal is not phase shifted relative to the portion ofthe comparative signal (i.e. the portion of the second portion of thecomparative signal) in the second portion of the second compositesignal. Examples of suitable light sensors include germanium photodiodes(PDs), and avalanche photodiodes (APDs).

The first light-combining component 211 combines the first portion ofthe comparative signal and the first portion of the reference signalinto a first composite signal. Due to the difference in frequenciesbetween the first portion of the comparative signal and the firstportion of the reference signal, the first composite signal is beatingbetween the first portion of the comparative signal and the firstportion of the reference signal.

The first light-combining component 211 also splits the first compositesignal onto a first detector waveguide 221 and a second detectorwaveguide 222. The first detector waveguide 221 carries a first portionof the first composite signal to a first light sensor 223 that convertsthe first portion of the second composite signal to a first electricalsignal. The second detector waveguide 222 carries a second portion ofthe second composite signal to a second light sensor 224 that convertsthe second portion of the second composite signal to a second electricalsignal. Examples of suitable light sensors include germanium photodiodes(PDs), and avalanche photodiodes (APDs).

In some instances, the light-combining component 211 splits the firstcomposite signal such that the portion of the comparative signal (i.e.the portion of the first portion of the comparative signal) included inthe first portion of the composite signal is phase shifted by 180°relative to the portion of the comparative signal (i.e. the portion ofthe first portion of the comparative signal) in the second portion ofthe composite signal but the portion of the reference signal (i.e. theportion of the first portion of the reference signal) in the firstportion of the composite signal is not phase shifted relative to theportion of the reference signal (i.e. the portion of the first portionof the reference signal) in the second portion of the composite signal.Alternately, the light-combining component 211 splits the compositesignal such that the portion of the reference signal (i.e. the portionof the first portion of the reference signal) in the first portion ofthe composite signal is phase shifted by 180° relative to the portion ofthe reference signal (i.e. the portion of the first portion of thereference signal) in the second portion of the composite signal but theportion of the comparative signal (i.e. the portion of the first portionof the comparative signal) in the first portion of the composite signalis not phase shifted relative to the portion of the comparative signal(i.e. the portion of the first portion of the comparative signal) in thesecond portion of the composite signal.

When the second light-combining component 212 splits the secondcomposite signal such that the portion of the comparative signal in thefirst portion of the second composite signal is phase shifted by 180°relative to the portion of the comparative signal in the second portionof the second composite signal, the light-combining component 211 alsosplits the composite signal such that the portion of the comparativesignal in the first portion of the composite signal is phase shifted by180° relative to the portion of the comparative signal in the secondportion of the composite signal. When the second light-combiningcomponent 212 splits the second composite signal such that the portionof the reference signal in the first portion of the second compositesignal is phase shifted by 180° relative to the portion of the referencesignal in the second portion of the second composite signal, thelight-combining component 211 also splits the composite signal such thatthe portion of the reference signal in the first portion of thecomposite signal is phase shifted by 180° relative to the portion of thereference signal in the second portion of the composite signal.

The first reference waveguide 210 and the second reference waveguide 208are constructed to provide a phase shift between the first portion ofthe reference signal and the second portion of the reference signal. Forinstance, the first reference waveguide 210 and the second referencewaveguide 208 can be constructed so as to provide a 90 degree phaseshift between the first portion of the reference signal and the secondportion of the reference signal. As an example, one reference signalportion can be an in-phase component and the other a quadraturecomponent. Accordingly, one of the reference signal portions can be asinusoidal function and the other reference signal portion can be acosine function. In one example, the first reference waveguide 210 andthe second reference waveguide 208 are constructed such that the firstreference signal portion is a cosine function and the second referencesignal portion is a sine function. Accordingly, the portion of thereference signal in the second composite signal is phase shiftedrelative to the portion of the reference signal in the first compositesignal, however, the portion of the comparative signal in the firstcomposite signal is not phase shifted relative to the portion of thecomparative signal in the second composite signal.

The first light sensor 223 and the second light sensor 224 can beconnected as a balanced detector and the first auxiliary light sensor218 and the second auxiliary light sensor 220 can also be connected as abalanced detector. For instance, FIG. 5B provides a schematic of therelationship between the electronics, the first light sensor 223, thesecond light sensor 224, the first auxiliary light sensor 218, and thesecond auxiliary light sensor 220. The symbol for a photodiode is usedto represent the first light sensor 223, the second light sensor 224,the first auxiliary light sensor 218, and the second auxiliary lightsensor 220 but one or more of these sensors can have otherconstructions. In some instances, all of the components illustrated inthe schematic of FIG. 5B are included on the LIDAR chip. In someinstances, the components illustrated in the schematic of FIG. 5B aredistributed between the LIDAR chip and electronics located off of theLIDAR chip.

The electronics connect the first light sensor 223 and the second lightsensor 224 as a first balanced detector 225 and the first auxiliarylight sensor 218 and the second auxiliary light sensor 220 as a secondbalanced detector 226. In particular, the first light sensor 223 and thesecond light sensor 224 are connected in series. Additionally, the firstauxiliary light sensor 218 and the second auxiliary light sensor 220 areconnected in series. The serial connection in the first balanceddetector is in communication with a first data line 228 that carries theoutput from the first balanced detector as a first data signal. Theserial connection in the second balanced detector is in communicationwith a second data line 232 that carries the output from the secondbalanced detector as a second data signal. The first data signal is anelectrical representation of the first composite signal and the seconddata signal is an electrical representation of the second compositesignal. Accordingly, the first data signal includes a contribution froma first waveform and a second waveform and the second data signal is acomposite of the first waveform and the second waveform. The portion ofthe first waveform in the first data signal is phase-shifted relative tothe portion of the first waveform in the first data signal but theportion of the second waveform in the first data signal being in-phaserelative to the portion of the second waveform in the first data signal.For instance, the second data signal includes a portion of the referencesignal that is phase shifted relative to a different portion of thereference signal that is included the first data signal. Additionally,the second data signal includes a portion of the comparative signal thatis in-phase with a different portion of the comparative signal that isincluded in the first data signal. The first data signal and the seconddata signal are beating as a result of the beating between thecomparative signal and the reference signal, i.e. the beating in thefirst composite signal and in the second composite signal.

The electronics 32 includes a transform mechanism 238 configured toperform a mathematical transform on the first data signal and the seconddata signal. For instance, the mathematical transform can be a complexFourier transform with the first data signal and the second data signalas inputs. Since the first data signal is an in-phase component and thesecond data signal its quadrature component, the first data signal andthe second data signal together act as a complex data signal where thefirst data signal is the real component and the second data signal isthe imaginary component of the input.

The transform mechanism 238 includes a first Analog-to-Digital Converter(ADC) 264 that receives the first data signal from the first data line228. The first Analog-to-Digital Converter (ADC) 264 converts the firstdata signal from an analog form to a digital form and outputs a firstdigital data signal. The transform mechanism 238 includes a secondAnalog-to-Digital Converter (ADC) 266 that receives the second datasignal from the second data line 232. The second Analog-to-DigitalConverter (ADC) 266 converts the second data signal from an analog formto a digital form and outputs a second digital data signal. The firstdigital data signal is a digital representation of the first data signaland the second digital data signal is a digital representation of thesecond data signal. Accordingly, the first digital data signal and thesecond digital data signal act together as a complex signal where thefirst digital data signal acts as the real component of the complexsignal and the second digital data signal acts as the imaginarycomponent of the complex data signal.

The transform mechanism 238 includes a transform component 268 thatreceives the complex data signal. For instance, the transform component268 receives the first digital data signal from the firstAnalog-to-Digital Converter (ADC) 264 as an input and also receives thesecond digital data signal from the first Analog-to-Digital Converter(ADC) 266 as an input. The transform component 268 can be configured toperform a mathematical transform on the complex signal so as to convertfrom the time domain to the frequency domain. The mathematical transformcan be a complex transform such as a complex Fast Fourier Transform(FFT). A complex transform such as a complex Fast Fourier Transform(FFT) provides an unambiguous solution for the shift in frequency ofLIDAR input signal relative to the LIDAR output signal that is caused bythe radial velocity between the reflecting object and the LIDAR chip.The electronics use the one or more frequency peaks output from thetransform component 268 for further processing to generate the LIDARdata (distance and/or radial velocity between the reflecting object andthe LIDAR chip or LIDAR system). The transform component 268 can executethe attributed functions using firmware, hardware or software or acombination thereof.

Although FIG. 5A through FIG. 5B illustrate light-combining componentsthat combine a portion of the reference signal with a portion of thecomparative signal, the processing component can include a singlelight-combining component that combines the reference signal with thecomparative signal so as to form a composite signal. As a result, atleast a portion of the reference signal and at least a portion of thecomparative signal can be combined to form a composite signal. Thecombined portion of the reference signal can be the entire referencesignal or a fraction of the reference signal and the combined portion ofthe comparative signal can be the entire comparative signal or afraction of the comparative signal.

As an example of a processing component that combines the referencesignal and the comparative signal so as to form a composite signal, FIG.5C illustrates the processing component of FIG. 5A modified to include asingle light-combining component. The comparative waveguide 196 carriesthe comparative signal directly to the first light-combining component211 and the reference waveguide 198 carries the reference signaldirectly to the first light-combining component 211.

The first light-combining component 211 combines the comparative signaland the reference signal into a composite signal. Due to the differencein frequencies between the comparative signal and the reference signal,the first composite signal is beating between the comparative signal andthe reference signal. The first light-combining component 211 alsosplits the composite signal onto the first detector waveguide 221 andthe second detector waveguide 222. The first detector waveguide 221carries a first portion of the composite signal to the first lightsensor 223 that converts the first portion of the second compositesignal to a first electrical signal. The second detector waveguide 222carries a second portion of the composite signal to the second lightsensor 224 that converts the second portion of the second compositesignal to a second electrical signal.

FIG. 5D provides a schematic of the relationship between theelectronics, the first light sensor 223, and the second light sensor 224of FIG. 5C. The symbol for a photodiode is used to represent the firstlight sensor 223, and the second light sensor 224 but one or more ofthese sensors can have other constructions. In some instances, all ofthe components illustrated in the schematic of FIG. 5D are included onthe LIDAR chip. In some instances, the components illustrated in theschematic of FIG. 5D are distributed between the LIDAR chip andelectronics located off of the LIDAR chip.

The electronics connect the first light sensor 223 and the second lightsensor 224 as a first balanced detector 225. In particular, the firstlight sensor 223 and the second light sensor 224 are connected inseries. The serial connection in the first balanced detector is incommunication with a first data line 228 that carries the output fromthe first balanced detector as a first data signal. The first datasignal is an electrical representation of the composite signal.

The electronics 32 include a transform mechanism 238 configured toperform a mathematical transform on the first data signal. Themathematical transform can be a real Fourier transform with the firstdata signal as an input. The electronics can use the frequency outputfrom the transform as described above to extract the LIDAR data.

Each of the balanced detectors disclosed in the context of FIG. 5Athrough FIG. 5D can be replaced with a single light sensor. As a result,the processing component can include one or more light sensors that eachreceives at least a portion of a composite signal in that the receivedportion of the composite signal can be the entire composite signal or afraction of the composite signal.

FIG. 5E shows an example of a relationship between the frequency of theLIDAR output signal and/or the system output signal, time, cycles anddata periods. Although FIG. 5E shows frequency versus time for only onechannel, the illustrated frequency versus time pattern can represent thefrequency versus time for each of the channels. The base frequency ofthe LIDAR output signal (f_(o)) can be the frequency of the LIDAR outputsignal at the start of a cycle.

FIG. 5E shows frequency versus time for a sequence of two cycles labeledcycle_(j) and cycle_(j+1). In some instances, the frequency versus timepattern is repeated in each cycle as shown in FIG. 5E. The illustratedcycles do not include re-location periods and/or re-location periods arenot located between cycles. As a result, FIG. 5E illustrates the resultsfor a continuous scan.

Each cycle includes K data periods that are each associated with aperiod index k and are labeled DP_(k). In the example of FIG. 5E, eachcycle includes three data periods labeled DP_(k) with k=1, 2, and 3. Insome instances, the frequency versus time pattern is the same for thedata periods that correspond to each other in different cycles as isshown in FIG. 5E. Corresponding data periods are data periods with thesame period index. As a result, each data period DP₁ can be consideredcorresponding data periods and the associated frequency versus timepatterns are the same in FIG. 5E. At the end of a cycle, the electronicsreturn the frequency to the same frequency level at which it started theprevious cycle.

During the data period DP₁, the electronics operate the light sourcesuch that the frequency of the LIDAR output signal changes by B₁ whereB₁≠0. The duration of the frequency change during DP, is represented byT₁ where T₁>0. During the data period DP₂, the electronics operate thelight source such that the frequency of the LIDAR output signal changesby B₂ where B₂≠0. The duration of the frequency change during DP₂ isrepresented by T₂ where T₂>0. The rate of frequency change during DP,can be represented by α₁ where α₁≠0. In FIG. 5E, the rate of frequencychange during DP₁ (α₁) is linear with a value of B₁/T₁. The rate offrequency change during DP₂ can be represented by α₂ where α₂≠0. In FIG.5E, the rate of frequency change during DP₂ (α₂) is linear with a valueof B₂/T₂. During the data period DP₃, the electronics operate the lightsource such that the frequency of the LIDAR output signal is constantfor the duration of the data period. The duration of DP₃ is representedby T₃ where T₃>0. The values of T₁, T₂, and T₃ can be the same ordifferent. In some instances, T₁=T₂. In one example, T₁=T₂≠T₃. Inanother example, T₁=T₂=T₃. In some instances, T₁≠T₂.

The beat frequency of all or a portion of the beating signals selectedfrom the first composite signal, the first data signal, the secondcomposite signal, and the second data signal during the data periodDP_(k) is F_(k) where k represents the data period index. For instance,when the processing component is constructed according to FIG. 5C andFIG. 5D, the beat frequency of the first composite signal and the firstdata signal is represented by F_(k). When the processing component isconstructed according to FIG. 5A and FIG. 5B, the beat frequency of thefirst composite signal, the first data signal, the second compositesignal, and the second data signal is represented by F_(k).

F₁ represents the beat frequency of the beating signals during the dataperiod DP₁. The value of F₁ can include a contribution from the distancebetween the LIDAR system and the reflecting object (f_(r,1)) and acontribution from the radial velocity between the LIDAR system and areflecting object (f_(d,1)). Accordingly, F₁ can be written asF₁=f_(r,1)+f_(d,1). The maximum possible value that can occur for F₁under normal operating conditions of the LIDAR system is represented byF_(1max).

The beat frequency of the beating signals during the data period DP₂ isrepresented by F₂. The value of F₂ can include a contribution from thedistance between the LIDAR system and a reflecting object (f_(r,2)) anda contribution from the radial velocity between the LIDAR system and thereflecting object (f_(d,2)). The maximum possible value that can occurfor F₂ under normal operating conditions of the LIDAR system isrepresented by F_(2max).

The beat frequency of the beating signals during the data period DP₃ isrepresented by F₃. The maximum possible value that can occur for F₃under normal operating conditions of the LIDAR system is represented byF_(3max). Since the frequency of the LIDAR output signal is constantduring the data period DP₃, F₃ will have contribution from the radialvelocity between the LIDAR system and the reflecting object (the Dopplerfrequency, f_(d,3)) but will not have a contribution from the distancebetween the LIDAR system and a reflecting object. As a result, the valueof F₃ can be set to the value of the Doppler frequency (f_(d,3)) wheref_(d,3)=2ν/λ with ν representing the radial velocity between the LIDARsystem and a reflecting object with direction from the reflecting objecttoward the LIDAR system being the positive direction, λ and representingthe wavelength of the LIDAR output signal. As a result, F₃=f_(d,3)=2ν/λand F_(3max)=f_(dmax)=2ν_(max)/λ where f_(dmax) represents the maximumvalue of the Doppler frequency during operation of the LIDAR systemunder normal conditions and ν_(max) represents the maximum value of theradial velocity (ν) during normal operating conditions.

A portion of the variables described above are disclosed in the contextof normal operating conditions. Normal operating conditions are theconditions for which the LIDAR system is designed to operate and arenormally set out in the specifications for the LIDAR system.Accordingly, when specifications are available, the value of ν_(max)would represent the largest radial velocity set forth in thespecifications. As another example, F_(1max) would represent the maximumin value of F₁ that can occur when operating the LIDAR system within theradial velocities and distances set forth in the specification.

The data period indices do not represent sequence in time. For instance,although FIG. 5E illustrates the cycles having DP₁ occurring before DP₂and DP₃; the cycles can have other arrangements of data periods.Examples of cycles with different data period arrangements include, butare not limited to, cycles where DP₁ occurs between DP₂ and DP₃ orcycles where DP₃ occurs before DP₂ with DP₂ occurring before DP₁.

Before operating the LIDAR system so as to generate LIDAR data, thevalues of one or more operating parameters can be selected and/orcalculated. The electronics can use the values identified for the one ormore parameters in the generated of the LIDAR data. An example of one ofthese parameters is the Analog-to-Digital Converters (ADC) sample rate(f_(samp)). The processing components include one or moreAnalog-to-Digital Converters such as the first Analog-to-DigitalConverter (ADC) 264 of FIG. 5A and FIG. 5C and the secondAnalog-to-Digital Converter (ADC) 266 of FIG. 5D. The one or moreAnalog-to-Digital Converters each receives one of the beating signalsand are each sampled at an ADC sample rate (f_(samp)). The ADC samplingrates (f_(samp)) required to generate useful LIDAR data in prior LIDARsystems results may be impractical to achieve; however, the LIDAR systemcan be operated such that the electronics undersample theAnalog-to-Digital Converter (ADC) 264 and/or the secondAnalog-to-Digital Converter (ADC) 266. The use of undersampling canpermit the use of practical sampling rates.

The ADC sample rate (f_(samp)) can be selected such thatf_(samp)≥2|F_(3max)|. Since F_(3max)=f_(dmax)=2ν_(max)/λ, the ADC samplerate (f_(samp)) can be selected such that f_(samp)≥2|F_(3max)|, orf_(samp)≥2|f_(dmax) or f_(samp)≥4ν_(max)/λ|. According to Nyquist'ssampling theorem, the sampling rate for an Analog-to-Digital Converters(ADC) should be greater than or equal to twice the highest frequency inthe beating signals. Accordingly, Nyquist's sampling theorem wouldprovide a sample rate (f_(samp)) according to: f_(samp)≥2*max|F_(1max),F_(2max), F_(3max)|. A beating signal is considered oversampled when thesampling rate is greater than 2*max F_(1max), F_(2max), F_(3max) andundersampled when sampling rate is less than 2*max|F_(1max), F_(2max),F_(3max)|. The value of f_(samp) can be selected so the signal isundersampled. For instance, f_(samp) can be selected such that2|F_(3max)|≤f_(samp)≤2*max|F_(1max), F_(2max), F_(3max)| or2|f_(dmax)|≤f_(samp)≤2*max|F_(1max), F_(2max), F_(3max)| or4|ν_(max)/λ|f_(samp)≤2*max|F_(1max), F_(2max), F_(3max)|.

Once an ADC sample rate (f_(samp)) is selected, the values for one ormore other parameters can be identified for use in generating LIDARdata. For instance, a frequency spectrum can be defined according toFIG. 5F. As shown in FIG. 5F, the value of F₁ can vary between 0.0 andF_(1max). The frequency range from −F_(1max) to F_(1max) can be dividedinto multiple zones that each has a length equal to f_(samp). Each ofthe zones is associated with a zone index of k_(k) where the subscript krepresents the data period index and each value of k_(k) is an integer.FIG. 5F illustrates the k_(k) values for data period DP1 (k₁). As shownin FIG. 5F, the value of k₁ can vary from −k_(1max) to k_(1max) toprovide a total of 2*k_(1max)+1 values for k₁. In FIG. 5F, k_(1max) hasa value of 2. The value for k_(1max) can be selected such that:(k_(1max)−0.5)f_(samp)≤F_(1max)<(k_(1max)+0.5)f_(samp).

The selected value of k_(1max) can be used to select a value forparameters p and q where p is an integer and q is an integer. The valuesof p and q are selected such that p<q, q>2k_(1max)+2, andp>q/(2k_(1max)+2). In some instances, p/q is an irreducible fraction.The selected values of p and q can be can be used to select B₁ and B₂such that B₂=+/−(p/q)*B₁ or when T₁≠T₂, such that α₂=+/−(p/q)*α₁.

During operation of the LIDAR system, the one or more Analog-to-DigitalConverters (ADCs) can each be sampled at a rate equal to f_(samp) andthe frequency output from the transform component 268 in response tosystem output signal output from the LIDAR system during the data periodDP₁ can serve as a value for F_(1,DC); the frequency output from thetransform component 268 in response to system output signal output fromthe LIDAR system during the data period DP₂ can serve as a value forF_(2,DC); and the frequency output from the transform component 268 inresponse to system output signal output from the LIDAR system during thedata period DP₃ can serve as the values of F_(3,DC).

The electronics can approximate the value of the contribution of theradial velocity between the LIDAR system and a reflecting object to thevalue F1 (f_(d,1)) as being equal to (f_(d,3)) and can approximate thevalue of the contribution of the radial velocity between the LIDARsystem and the reflecting object to the value of F2 (f_(d,2)) as beingequal to (f_(d,3)). Accordingly, the electronics can setf_(d,1)=f_(d,2)=f_(d,3). As noted above, f_(d,3)=F₃. Further, theelectronics can approximate the value of F₃ as being equal to F_(3,DC)because F_(3DC) is not a result of undersampling becausef_(samp)≥2|F_(3max)| which satisfies the Nyquist's sampling theoremduring the data period DP₃. As a result, the electronics can approximatef_(d,1)=f_(d,2)=f_(d,3)=F₃=F_(3,DC)=f_(d).

Because of the undersampling of the ADC, there are multiple possiblevalues for the contribution of the distance between the LIDAR system andthe reflecting object to the value of F₁ (f_(r,1)) and there aremultiple possible values for the contribution of the distance betweenthe LIDAR system and the reflecting object to the value of F₂ (f_(r,2)).The electronics can determine the possible values of f_(r,1) for dataperiod DP₁ and the possible values of f_(r,2) for the data period DP₂.Each of the different possible values can be represented by f_(r,k,n,e)where k represents the data period index, n is a possible value index inthe range of −k_(1max)≤n≤k_(1max) where each value of n is an integer,and e represents an equation index that identifies the equation fromwhich the possible value was generated. The electronics can determine aseries of possible values for the data period DP₁ from the followingEquation 1A: f_(r,1,n,A)=F_(1,DC)+f_(d)+n*f_(samp) where−k_(1max)≤n≤k_(1max). Accordingly, there can be 2*k_(1max)+1 values forf_(r,1,n,e). The electronics can determine a series of possible valuesfor the data period DP₂ from the following Equation 2A:f_(r,2,n,A)=(F_(2,DC)+f_(d))*(q/p)+n*f_(samp)*(q/p) when the rate offrequency change during DP₂ (α₂) is positive or Equation 2B:f_(r,2,n,B)=−(F_(2,DC)+f_(d))*(q/p)−n*f_(samp)*(q/p) when the rate offrequency change during DP₂ (α₂) is positive where −k_(1max)≤n≤k_(1max).Accordingly, there can be (2*k_(1max)+1) values for f_(r,2,n,e).

One of the possible values of f_(r) determined from the data period DP₁(f_(r,1,n,A) above) will match or substantially match one of thepossible values of f_(r) determined from the data period DP₂(f_(r,2,n,A) and f_(r,2,n,B)). The electronics can identify the matchingpair. As a result of the conditions for selecting p and q, there will beonly one matching pair for each cycle for values of n in the range of−k_(1max)≤n≤k_(1max). Values of n outside of this range can produceother matches. The value of f_(r) for the matching pair serves as thevalue of f_(r) for the cycle.

The electronics can use the values determined for f_(r) and/or f_(d) todetermine the LIDAR data for the cycle. For instance, the electronicscan quantify the distance between the object and the LIDAR system fromc*f_(r)*T/(2*B₁) and/or the radial velocity between the object and theLIDAR system from ν=λ*f_(d)/2.

Although FIG. 5D illustrates three data periods, the number of dataperiods can be different. For instance, the data period DP₃ can beoptional when the reflecting objects are stationary relative to theLIDAR system (i.e. ν=0.0). In these instances, the LIDAR data can begenerated as disclosed above withf_(d,1)=f_(d,2)=f_(d,3)=f_(3,DC)=f_(d)=0.0.

Suitable platforms for the LIDAR chips include, but are not limited to,silica, indium phosphide, and silicon-on-insulator wafers. FIG. 6 is across-section of portion of a chip constructed from asilicon-on-insulator wafer. A silicon-on-insulator (SOI) wafer includesa buried layer 310 between a substrate 312 and a light-transmittingmedium 314. In a silicon-on-insulator wafer, the buried layer 310 issilica while the substrate 312 and the light-transmitting medium 314 aresilicon. The substrate 312 of an optical platform such as an SOI wafercan serve as the base for the entire LIDAR chip. For instance, theoptical components shown on the LIDAR chips of FIG. 1A through FIG. 1Dcan be positioned on or over the top and/or lateral sides of thesubstrate 312.

FIG. 6 is a cross section of a portion of a LIDAR chip that includes awaveguide construction that is suitable for use in LIDAR chipsconstructed from silicon-on-insulator wafers. A ridge 316 of thelight-transmitting medium extends away from slab regions 318 of thelight-transmitting medium. The light signals are constrained between thetop of the ridge 316 and the buried oxide layer 310.

The dimensions of the ridge waveguide are labeled in FIG. 6. Forinstance, the ridge has a width labeled w and a height labeled h. Athickness of the slab regions is labeled T. For LIDAR applications,these dimensions can be more important than other dimensions because ofthe need to use higher levels of optical power than are used in otherapplications. The ridge width (labeled w) is greater than 1 μm and lessthan 4 μm, the ridge height (labeled h) is greater than 1 μm and lessthan 4 μm, the slab region thickness is greater than 0.5 μm and lessthan 3 μm. These dimensions can apply to straight or substantiallystraight portions of the waveguide, curved portions of the waveguide andtapered portions of the waveguide(s). Accordingly, these portions of thewaveguide will be single mode. However, in some instances, thesedimensions apply to straight or substantially straight portions of awaveguide. Additionally or alternately, curved portions of a waveguidecan have a reduced slab thickness in order to reduce optical loss in thecurved portions of the waveguide. For instance, a curved portion of awaveguide can have a ridge that extends away from a slab region with athickness greater than or equal to 0.0 μm and less than 0.5 μm. Whilethe above dimensions will generally provide the straight orsubstantially straight portions of a waveguide with a single-modeconstruction, they can result in the tapered section(s) and/or curvedsection(s) that are multimode. Coupling between the multi-mode geometryto the single mode geometry can be done using tapers that do notsubstantially excite the higher order modes. Accordingly, the waveguidescan be constructed such that the signals carried in the waveguides arecarried in a single mode even when carried in waveguide sections havingmulti-mode dimensions. The waveguide construction disclosed in thecontext of FIG. 6 is suitable for all or a portion of the waveguides onLIDAR chips constructed according to FIG. 1A through FIG. 1D.

Light sensors that are interfaced with waveguides on a LIDAR chip can bea component that is separate from the chip and then attached to thechip. For instance, the light sensor can be a photodiode, or anavalanche photodiode. Examples of suitable light sensor componentsinclude, but are not limited to, InGaAs PIN photodiodes manufactured byHamamatsu located in Hamamatsu City, Japan, or an InGaAs APD (AvalanchePhoto Diode) manufactured by Hamamatsu located in Hamamatsu City, Japan.These light sensors can be centrally located on the LIDAR chip.Alternately, all or a portion the waveguides that terminate at a lightsensor can terminate at a facet located at an edge of the chip and thelight sensor can be attached to the edge of the chip over the facet suchthat the light sensor receives light that passes through the facet. Theuse of light sensors that are a separate component from the chip issuitable for all or a portion of the light sensors selected from thegroup consisting of the first auxiliary light sensor 218, the secondauxiliary light sensor 220, the first light sensor 223, and the secondlight sensor 224.

As an alternative to a light sensor that is a separate component, all ora portion of the light sensors can be integrated with the chip. Forinstance, examples of light sensors that are interfaced with ridgewaveguides on a chip constructed from a silicon-on-insulator wafer canbe found in Optics Express Vol. 15, No. 21, 13965-13971 (2007); U.S.Pat. No. 8,093,080, issued on Jan. 10, 2012; U.S. Pat. No. 8,242,432,issued Aug. 14, 2012; and U.S. Pat. No. 6,108,8472, issued on Aug. 22,2000 each of which is incorporated herein in its entirety. The use oflight sensors that are integrated with the chip are suitable for all ora portion of the light sensors selected from the group consisting of theauxiliary light sensor 218, the second auxiliary light sensor 220, thefirst light sensor 223, and the second light sensor 224.

The light source 10 that is interfaced with the utility waveguide 12 canbe a laser chip that is separate from the LIDAR chip and then attachedto the LIDAR chip. For instance, the light source 10 can be a laser chipthat is to the chip using a flip-chip arrangement. Use of flip-chiparrangements is suitable when the light source 10 is to be interfacedwith a ridge waveguide on a chip constructed from silicon-on-insulatorwafer. Alternately, the utility waveguide 12 can include an opticalgrating (not shown) such as Bragg grating that acts as a reflector foran external cavity laser. In these instances, the light source 10 caninclude a gain element that is separate from the LIDAR chip and thenattached to the LIDAR chip in a flip-chip arrangement. Examples ofsuitable interfaces between flip-chip gain elements and ridge waveguideson chips constructed from silicon-on-insulator wafer can be found inU.S. Pat. No. 9,705,278, issued on Jul. 11, 2017 and in U.S. Pat. No.5,991,484 issued on Nov. 23, 1999; each of which is incorporated hereinin its entirety. When the light source 10 is a gain element or laserchip, the electronics 32 can change the frequency of the outgoing LIDARsignal by changing the level of electrical current applied to throughthe gain element or laser cavity.

Suitable electronics 32 can include, but are not limited to, acontroller that includes or consists of analog electrical circuits,digital electrical circuits, processors, microprocessors, digital signalprocessors (DSPs), Field Programmable Gate Arrays (FPGAs), computers,microcomputers, or combinations suitable for performing the operation,monitoring and control functions described above. In some instances, thecontroller has access to a memory that includes instructions to beexecuted by the controller during performance of the operation, controland monitoring functions. Although the electronics are illustrated as asingle component in a single location, the electronics can includemultiple different components that are independent of one another and/orplaced in different locations. Additionally, as noted above, all or aportion of the disclosed electronics can be included on the chipincluding electronics that are integrated with the chip.

Other embodiments, combinations and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. Therefore, this invention is to be limited only by thefollowing claims, which include all such embodiments and modificationswhen viewed in conjunction with the above specification and accompanyingdrawings.

1.


1. A LIDAR system, comprising: an Analog-to-Digital Converter (ADC) thatreceives a beating signal that beats a first signal against a secondsignal, the first signal being generated from light that has exited fromthe LIDAR system and returned to the LIDAR system after being reflectedby an object located outside of the LIDAR system, the second signalbeing generated from light that has not exited from the LIDAR system, afrequency of the beating signal having a frequency contribution from aseparation between the LIDAR system and the object; and electronics thatgenerate multiple first possible frequency values that are each acandidate for a value of the frequency contribution.
 2. The system ofclaim 1, wherein the electronics identify the first possible frequencyvalue that represents a value of the frequency contribution from theseparation between the LIDAR system and the object.
 3. The system ofclaim 1, wherein the electronics that generate multiple second possiblefrequency values that are each a candidate for a value of the frequency.4. The system of claim 3, wherein only one of the first possiblefrequency values matches one of the second possible frequency values. 5.The system of claim 4, wherein electronics identify the first possiblefrequency value that matches one of the second possible frequencyvalues.
 6. The system of claim 5, wherein the electronics use theidentified frequency values to quantify a distance between the objectand the LIDAR system.
 7. The system of claim 1, wherein the electronicssample the Analog-to-Digital Converter (ADC) so as to generate a digitaldata signal and use the digital data signal to quantify a distancebetween the object and the LIDAR system.
 8. The system of claim 7,wherein the electronics undersample the Analog-to-Digital Converter(ADC).
 9. The system of claim 1, wherein the light that has exited fromthe LIDAR system is included in a system output signal, the electronicscontrol a frequency of the system output signal over a series of cycles,the cycles include multiple data periods, the electronics change thefrequency of the system output signal at a first rate during a first oneof the data periods, the electronics change the frequency of the systemoutput signal at a second rate during a second one of the data periods,the second rate is less than the first rate.
 10. The system of claim 9,wherein the second rate can be expressed as: α₂=+/−(p/q)*α₁ where α₂represents the second rate, α₁ represents the first rate, p is aninteger, q is an integer, and p<q, and p/q is an irreducible fraction.11. The system of claim 10, wherein q>2k_(1max)+2 and p>q/(2k_(1max)+2)wherein k_(1max) is an integer.
 12. The system of claim 11, whereink_(1max) is selected such that(k_(1max)−0.5)f_(samp)≤F_(1max)≤(k_(1max)+0.5)f_(samp) where f_(samp)represents a sampling rate of the Analog-to-Digital Converter (ADC) andF_(1max) represents a maximum possible value of the beating signalduring the first period.
 13. A LIDAR system, comprising: a transmitterconfigured to output a LIDAR output signal from the LIDAR system; andelectronics that control a frequency of the system output signal over aseries of cycles, the cycles include multiple data periods, theelectronics changing the frequency of the system output signal at afirst rate during a first one of the data periods, the electronicschanging the frequency of the system output signal at a second rateduring a second one of the data periods, the second rate being less thanthe first rate.
 14. The system of claim 13, wherein the second rate canbe expressed as: α₂=+/−(p/q)*α₁ where α₂ represents the second rate, α₁represents the first rate, p is an integer, q is an integer, and p<q.15. The system of claim 14, wherein p/q is an irreducible fraction. 16.The system of claim 14, wherein q>2k_(1max)+2 wherein k_(1max) is aninteger.
 17. The system of claim 16, wherein p>q/(2k_(1max)+2).
 18. Thesystem of claim 17, wherein k_(1max)>0.
 19. The system of claim 14,wherein α₂=B₂/T and α₁=B₁/T where T represents a duration of the firstdata period, B₁ represents a frequency change of the system outputsignal during the first data period and B₂ represents a frequency changeof the system output signal during the second data period.
 20. A methodof operating a LIDAR system, comprising: receiving a beating signal atan Analog-to-Digital Converter (ADC), the beating signal beating a firstsignal against a second signal, the first signal being generated fromlight that has exited from the LIDAR system and returned to the LIDARsystem after being reflected by an object located outside of the LIDARsystem, the second signal being generated from light that has not exitedfrom the LIDAR system, a frequency of the beating signal having afrequency contribution from a separation between the LIDAR system andthe object; and generating multiple first possible frequency values thatare each a candidate for a value of the frequency contribution.